The mother of a Briton being held by Russian authorities who boarded a Greenpeace protest ship in the Arctic says she is worried by reports he could be charged with piracy.

Sue Turner, 62, said she has yet to hear from engineer Iain Rogers, 37, one of six British citizens on board the Arctic Sunrise, amid reports that charges will be brought following protests against oil drilling.

Lawyers for Greenpeace International have demanded immediate access to its members on board the ship, which has been towed close to the north-west port of Murmansk after armed Russians took control of it last Thursday.

Speaking from her home in Exeter, Mrs Turner said she was worried because she has had no news of her son.

"If they charge them with piracy there is a 15-year jail sentence and a £10,000 fine," she said.

"I'm not so concerned by the fine, we can get around that. But Russian prisons are not the nicest places to be. They might deport them straight away, they might charge them and then imprison them a while, I don't know. We have to wait and see."

Mr Rogers, who lives on a boat in Portugal, has been working as an engineer on the Arctic Sunrise since it headed to the region in the summer, she said.

Mrs Turner praised Greenpeace, saying it was working hard to get news of the people held. The 30 activists on the ship are from 18 countries.

Russian investigators have told reporters they will file piracy charges against an unspecified number of activists who tried to climb on to an offshore drilling platform owned by state-controlled gas company Gazprom. Two activists tried to climb on to the Prirazlomnaya platform on Thursday and others assisted from small inflatable boats.

Greenpeace said that Russian officials had merely opened a criminal investigation, which did not necessarily mean they would bring charges.